The broad purpose of this program is to continue the study of various factors responsible for the regulation of acid excretion by the kidney. Particular emphasis will be placed on the influence of extracellular volume and of the anion composition of the glomerular filtrate on hydrogen ion secretion in the distal nephron. The specific questions to be addressed include: a. The role of distal sodium avidity, as influenced by salt active hormones, in regulating distal sodium -- hydrogen exchange during hypotonic volume expansion. 1. Does hypotonic volume expansion increase aldosterone secretion? 2. Does spironalactone interfere with the ability of hypotonic volume expansion to repair metabolic acidosis. 3. Does adrenalectomy interfere with the ability of hypotonic volume expansion to repair metabolic acidosis. b. The role of distal sodium avidity, as influenced by salt active hormones, in the control of acid excretion in the normal and acid-challenged animal. 1. Does aldosterone play a role in the maintenance of normal acid-base equilibrium. 2. Does aldosterone play an important role in the response to an acid challenge. c. The role of distal delivery, as influenced by filtrate anion composition, and of distal cation stores in the control of acid excretion. 1. Does the character of the accompanying anion influence the rate of recovery from an acute acid challenge? 2. What is the nature of the interaction between the filtered load of chloride and of non-reabsorbable anion in the regulation of acid excretion during acid feeding? 3. Does the availability of sodium and potassium for excretion influence the response to mineral acid feeding? 4. What is the upper limit for distal hydrogen ion secretion during acid loading.